buildFile << """
            abstract class ToolchainTask extends DefaultTask {
                @Nested
                abstract Property<JavaLauncher> getLauncher1()
                @Nested
                abstract Property<JavaLauncher> getLauncher2()
                @OutputFile
                abstract RegularFileProperty getOutputFile()

                @TaskAction
                void myAction() {

            getLauncher().convention(service.launcherFor(spec -> {}));
        }
    }

    @TaskAction
    public void validateTaskClasses() throws IOException {
        getWorkerExecutor()
            .processIsolation(spec -> {
                if (getLauncher().isPresent()) {
                    spec.getForkOptions().setExecutable(getLauncher().get().getExecutablePath());
                } else {

import javax.inject.Inject;

// tag::custom-toolchain-task-with-java[]
abstract class CustomTaskUsingToolchains extends DefaultTask {

    @Nested
    abstract Property<JavaLauncher> getLauncher() // <1>

    CustomTaskUsingToolchains() {
        def toolchain = project.extensions.getByType(JavaPluginExtension.class).toolchain // <2>
        Provider<JavaLauncher> defaultLauncher = getJavaToolchainService().launcherFor(toolchain) // <3>

            this(session.getLauncher(), session::close);
        }

        BackwardsCompatibleLauncherSession(Launcher launcher, Runnable onClose) {
            this.launcher = launcher;
            this.onClose = onClose;
        }

        Launcher getLauncher() {
            return launcher;
        }

        @Override

        buildScript """
            apply plugin: JvmToolchainsPlugin

            abstract class UnpackLauncher extends DefaultTask {
                @Nested
                abstract Property<JavaLauncher> getLauncher()

                @TaskAction
                void useLauncher() {
                    // we never get here
                    launcher.getOrNull()
                }
            }

            task.getClasspath().setFrom((Callable<Object>) () -> extension.getPluginSourceSet().getCompileClasspath());

            task.getLauncher().convention(toolchainLauncher(project));
        });
        project.getTasks().named(JavaBasePlugin.CHECK_TASK_NAME, check -> check.dependsOn(validatorTask));
    }